Master information carrier, process for producing the carrier, and method and apparatus for recording master information signal on magnetic recording medium by using the carrier

ABSTRACT

A master information carrier comprises a substrate whose surface has an embossed pattern corresponding to an information signal. At least a surface of the protruding portion of the embossed pattern is made of a ferromagnetic material. A method for writing an information signal into a sheet or disk magnetic record medium with a ferromagnetic thin film or coating is performed by putting the surface of the magnetic record medium into contact with the master information carrier so as to write a magnetized pattern corresponding to the embossed pattern of the master information carrier into the magnetic record medium.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for recordinginformation signals into a magnetic record medium used in a device formagnetic recording and reproduction with high recording density andlarge capacity, a master information carrier to be used for therecording method, and a method for making the master informationcarrier.

BACKGROUND OF THE INVENTION

Recently, a magnetic recording and reproduction apparatus has beenincreasing recording density to realize small size and large capacity.Especially, in the field of a hard disk as a typical magnetic recordingdevice, an areal recording density of more than one gigabit per squareinch is already available on the market, and an areal recording densityof ten gigabits per square inch is expected in a couple of years. Thetechnology proceeds with a rapid pace.

One of the primary factors that has enabled such high recording densityis the increasing linear recording density, due to improvements ofmedium properties, head-disk interface performance, and new signalprocessing method such as “partial response”. However, in recent years,the rate of increase in track density exceeds that of linear recorddensity, and thus becomes a primary factor of the increasing arealrecording density. Practical use of a magneto-resistive type head, whichis superior to a conventional inductive type head in read-back signalperformance, has contributed to the progress in the track density. It ispossible at present to read a signal from a track whose width is only afew microns with good SIN ratio by practical use of themagneto-resistive type head. On the other hand, it is expected that atrack pitch will reach the sub-micron range in the near future alongwith further improvement of the head performance.

A tracking servo technique is important for the head to read a signalwith high S/N ratio by tracing such a narrow track. For example, aconventional hard disk has areas that are located at predeterminedangles over 360 degree and in which information such as a tracking servosignal, address and clock signal are written. In this specification,preformat writing or prewriting of such an information signal is calleda “preformat recording”. A head can trace a track by reading suchinformation in predetermined intervals, and monitoring and correctingthe head position.

The above mentioned tracking servo signal, address and clock signalbecome reference signals for the head to trace a track precisely.Therefore, precise record positions are required for these informationsignals. Current preformat recording into a hard disk is usuallyperformed by magnetic heads placed in the hard disk drive by using aspecial servo track writer after installing the disk and the head intothe drive. In this case, a required accuracy of the track position forwriting is achieved by precisely controlling the position of the headincorporated in the drive by using an external actuator equipped to theservo track writer.

Such a preformat recording of servo signal, address information andclock signal is performed similarly for large capacity flexible disks ordisk cartridges, which are removable disk media seen in the marketrecently, by using a magnetic head and a servo writer. These media areremovable, so they can be compatibly used by other drives. Therefore, itis not always required to perform the preformat writing by the heads ofeach drive after incorporating the heads into the drive though it isrequired for a normal hard disk. However, these removable disks aresimilar to normal hard disks from the viewpoint that the preformatwriting is performed by precisely controlling the position of the headby using an external actuator equipped to the servo track writer.

However, in the present preformat recording of servo signal, addressinformation and clock signal, there are the problems described below.

The first problem is that writing with the magnetic head is a linearrecording relying on relative movement between the magnetic head and therecording medium. This means that a long period is required forpreformat writing by the above-mentioned method, while preciselycontrolling the position of the magnetic head with a servo track writer.Moreover, because the servo writer is expensive, the cost for preformatwriting is high.

This problem becomes even more serious as the areal recording densityincreases. This is not only caused by an increase of tracks in radialdirection. As the track density increases, a higher precision isrequired for the head positioning and as a result, servo areas, in whichthe tracking servo signal and other signals are recorded, have to beprovided with smaller angular distances between them over 360 degrees.Moreover, the address information to be written as the preformat dataincreases as the recording density increases. Thus more time and costare required for writing more information signals as the record densitybecomes higher.

A smaller size for magnetic disks is expected to be the trend on themarket. However, large disks of 3.5 or 5 inch size are still in demand.These large disks require more information signals to be written for thepreformat than the small disks. The necessary time for preformat writinginfluences the cost effectiveness of such large disks.

The second problem is that a space between the head and a medium or adiffusive recording magnetic field due to a pole shape of the recordhead does not make a steep magnetic transition at track edges where thepreformat data is written. Relative movement between the magnetic headand a medium is indispensable in writing with the head, so some space isnecessary between the head and the medium for interface performancebetween them. A conventional magnetic head usually has two elements forwriting and reading. A pole width at a trailing edge of the headcorresponds to a record track width, and a pole width at a leading edgeis several times larger than that at the trailing edge.

The above two phenomena may be a factor for causing the diffusiverecording magnetic field to fringe over the preformatted record trackwidth, resulting in the magnetic transition at track edges not beingsteep or erased areas appearing on both sides of a track. In currenttracking servo techniques, the head position is detected by a change inread signal amplitude when the head misses a track. Therefore, as in theprocess of reproducing the data signal recorded between the servotracks, the system requires not only a high S/N ratio of a read signalwhen the head traces a track correctly, but also a steep off-trackperformance, in which the read signal amplitude changes steeply as thehead misses the track. If the magnetic transition is not steep enough atan edge of a track where the preformat is written, it is difficult torealize a precise tracking servo performance that will be required for asubmicron track recording in the future.

As a solution of the first of the two problems mentioned above, aduplicate record technique of a tracking servo signal or other signalsby using a magnetic transfer technique has been disclosed in JapanesePublication of Unexamined Patent Application (Tokukai) Sho63-183623. Theduplicate record technique of a magnetized pattern using the magnetictransfer technique was originally developed as a method for copying thecontents of a videotape. This technique is explained in detail in C. D.Mee and E. D. Daniel, “Magnetic Recording”, Vol. 3, Chapter 2, p94-105,for example. The method disclosed in Tokukai Sho63-183623 applies theabove duplication technique for videotape to the preformat writing ofthe tracking servo signal or other signals for a flexible disk.

Such a magnetic transfer technique may improve the productivity of thepreformat writing. However, this technique is effective only for mediasuch as flexible disks that have a small coercive force and a low arealrecord density. It is not effective for today's hard disks, which have alarge coercive force and a high areal record density in the order ofseveral hundred megabits to gigabit.

In the magnetic transfer technique, an alternating bias magnetic fieldhas to be applied, whose amplitude is approximately 1.5 times thecoercive force of the target (slave) disk to ensure high transferefficiency. The coercive force of the master disk should be more thanthree times of that of the slave disk, so that the master information,i.e. a magnetized pattern in the master disk, is not erased by thealternating bias magnetic field. Today's high-density hard disk mediahave a coercive force of 120-200 kA/m to enable a high-areal recordingdensity. It is estimated that the coercive force will reach 250-350 kA/mfor an areal record density of 10 gigabit order in the future. Thismeans that a master disk should have a very large coercive force of360-600 kA/m at present and 750-1050 kA/m in the future.

It is difficult to realize such a large coercive force for a master diskfrom the standpoint of a magnetic material. In addition, masterinformation cannot be written into a master disk having such a largecoercive force by any current magnetic recording method. Therefore,considering a possible coercive force for a master disk in the currentmagnetic transfer technique, the coercive force of the slave diskinevitably has an upper limit.

In the above-mentioned magnetic transfer technique, it is possible toutilize a thermo-magnetic transfer technique, where instead of applyingthe alternating bias magnetic field to the slave disk, the slave disk isheated to the temperature near to the Curie temperature for eliminatingspontaneous magnetization. However, in that case, the Curie temperatureof the slave disk should be much lower than that of the master disk.High coercive force magnetic film composed of Co group materials usedfor a high density magnetic record medium has a relatively high Curietemperature, so it is difficult to realize the characteristics requiredof the master disk and the slave disk for the thermo-magnetic transfer.Therefore, this preformat writing with a magnetic transfer techniquecannot be a substantial solution for the before-mentioned problems.

Another solution for these problems is a pre-embossed disk techniquedisclosed in Publication of Japanese Unexamined Patent Application(Tokukai) Hei7-153060 (corresponding to U.S. Pat. No. 5,585,989 andEuropean laid open patent application Ser. No. 655,734). In thistechnique, an embossed pattern corresponding to a tracking servo signal,address, clock signal and/or other signals is formed on a surface of thedisk substrate by a stamper, and a magnetic film is formed on thesubstrate. This technique can be an effective solution for thebefore-mentioned problems. However, the embossed pattern on the disksurface may influence the head's flying float performance (or contactstate in the case of contact writing) when writing or reading, so thatinterface performance between the head and medium may be problematic. Inaddition, the substrate processed by the stamper is usually a polymermaterial (plastic), so it cannot be heated when forming the magneticfilm for ensuring medium properties, and thus a necessary S/N ratiocannot be ensured.

As mentioned above, a truly effective solution of the before-mentionedtwo problems, which does not sacrifice other important performance suchas the medium S/N ratio or the head-medium interface, has not been foundyet.

SUMMARY OF THE INVENTION

Considering the above problems, the present invention provides a methodand apparatus for improving the productivity of the preformat writingand the sharpness of the magnetic transition at edges of a track wherethe preformat is written, without sacrificing other importantperformance criteria such as the S/N ratio or the head-medium interface.

A method for writing a master information signal into a magnetic recordmedium according to the present invention uses a master informationcarrier comprising a substrate; an embossed pattern corresponding to themaster information signal formed on the substrate; and a ferromagneticmaterial that forms at least the surface of the protruding portion ofthe embossed pattern. The surface of this master information carriercontacts with a surface of a target magnetic record medium having asheet or disk shape, whose surface has a ferromagnetic thin film orcoating. Thus, a magnetized pattern corresponding to the embossedpattern on the surface of the master information carrier is recordedinto the magnetic record medium.

It is preferable that the ferromagnetic material forming the surface ofthe protruding portion is a soft magnetic material. Alternatively, itcan be a hard or semihard magnetic material whose coercive force is lessthan 40 kA/m in the in-plane or perpendicular direction of thesubstrate.

It is more preferable to apply a direct (i.e., not alternating) magneticfield for exciting the ferromagnetic material forming the surface of theprotruding portion, or an alternating magnetic field for assisting thewriting of the magnetizing pattern, when the surface of the masterinformation carrier contacts with the surface of the magnetic recordmedium.

According to the above-mentioned method of the present invention, aleakage flux is generated from the ferromagnetic material at theprotruding portion of the surface of the master information carrier whenthe ferromagnetic material is magnetized in one direction. This leakageflux performs writing of the magnetized pattern corresponding to theembossed pattern of the master information carrier into the magneticrecord medium. Thus, the preformat writing of the tracking servo signal,address signal, clock signal and other signals is achieved by using theembossed pattern formed on the surface of the master informationcarrier, corresponding to the information signal.

The writing method of the present invention utilizes a leakage magneticfield generated from the ferromagnetic material at the protrudingportion due to the change of the magnetic reluctance through theembossed pattern. Therefore, the writing mechanism is the same as aconventional magnetic record utilizing a leakage magnetic fieldgenerated from a gap of the magnetic head. However, in the writingmethod of the present invention, the master information of the wholeplane of the master information carrier is written into the magneticrecord medium at one time without relative movement between the masterinformation carrier and the record medium. This characteristic pointdiffers from the writing with magnetic head in the prior art, in whichthe head and the record medium move relative to each other. Thischaracteristic point of the present invention provides an effectivesolution for the previously mentioned two problems, as follows.

First, the time needed for the preformat writing is substantially shortcompared with the prior art using a magnetic head. In addition, anexpensive servo-tracking writer is not necessary for precise positioncontrol of the magnetic head. Therefore, the present invention canimprove the productivity of the preformat writing and reduce productioncosts.

Secondly, a space gap between the master information carrier and themagnetic record medium can be minimized, since relative movement betweenthem is not required for writing the information signal. In addition,the leakage magnetic field for writing does not diffuse, while itdiffuses fringing over the record track width in the prior art using amagnetic head due to a pole shape of the magnetic head. Thus themagnetic transition at edges of a track into which the preformat data iswritten has sharpness compared with the writing with a magnetic head.This ensures a precise tracking of a head in reading data signals fromthe magnetic record medium.

Furthermore, the method of the present invention does not require thelimitation of a structure or magnetic performance of the magnetic recordmedium in which the master information is written, differently from themagnetic transfer technique disclosed in Tokukai Sho63-183623 or thepre-embossed disk technique disclosed in Tokukai Hei7-153060 aspreviously stated.

For example, in the magnetic transfer technique disclosed in TokukaiSho63-183623, the master disk requires a substantially high recordresolution, since the master disk itself is a magnetic record mediumhaving master information as a magnetization pattern of the master disk.Consequently, the magnetic flux density and the film thickness cannot beenhanced sufficiently for enlarging magnetic field intensity formagnetic transfer. In addition, a gradient of the magnetic field for themagnetic transfer becomes small in the magnetic transition area sincedemagnetization occurs due to the repelling poles of the di-bit. Toensure a sufficient magnetic transfer efficiency with such a weakmagnetic field for magnetic transfer, an alternating bias magnetic fieldis applied, which has an intensity of approximately 1.5 times of acoercive force of the target (slave) record disk. Therefore, thismagnetic transfer technique can be applied only to a flexible disk orother medium with low record density since the coercive force is limitedas previously stated.

On the contrary, the master information carrier of the present inventionhas the master information as an embossed pattern, and a leakagemagnetic field, which is generated from a ferromagnetic material at aprotruding portion of the embossed pattern due to a change of a magneticreluctance through the embossed pattern, performs the magnetic recordingof the master information. The master information carrier does notrequire a high resolution as the magnetic record medium, though it isrequired for the master disk in the magnetic transfer technique.Therefore a magnetic flux density and a thickness of the ferromagneticmaterial that forms the protruding portion of the surface of the masterinformation carrier can be as large as the magnetic record head used inthe prior art, so that a sharp and large recording magnetic field can beobtained similarly to a magnetic record head. Thus, a sufficient writingability can be obtained for any magnetic record medium, including ausual flexible disk and hard disk and a record medium with a highcoercive force for a gigabit recording in the future.

The pre-embossed disk technique disclosed in Tokukai Hei7-153060 mayrequire a sacrifice of the medium S/N ratio relating to a substratetemperature at film formation process and the head-medium interfaceperformance relating to a head floating performance (or contactingstate), since the substrate material and shape of the disk arerestricted as previously explained. On the contrary, the writing methodof the present invention has no limitation about the substrate materialand surface shape of the disk to be written for the preformat.

As mentioned above, the writing method of the present invention providesan essential solution for the previously mentioned two problems withoutsacrificing other important performances such as the medium S/N ratioand interface performance.

It is also effective in this writing method to apply an alternating anddecaying bias magnetic field for obtaining higher writing efficiency. Inthis case, there is no possibility of erasing a master information bythe alternating magnetic field or other external magnetic field sincethe master information is formed by the embossing pattern in the masterinformation carrier of the present invention differently from the masterinformation written as a magnetization pattern in the magnetic transfertechnique. Therefore, the coercive force of the ferromagnetic materialthat forms the protruding portion of the surface of the masterinformation carrier has no limitation. The ferromagnetic material is notlimited to a material with high coercive force, but can be selected froma variety of materials such as a semihard magnetic material or a softmagnetic material as long as the material can generate sufficientmagnetic field for writing the master information into a magnetic recordmedium.

In the writing method of the present invention, the ferromagneticmaterial that forms the protruding portion of the surface of the masterinformation carrier should be magnetized in one direction to generate amagnetic field for writing. Therefore, if the semihard or soft magneticmaterial used as the ferromagnetic material cannot generate a stableone-way magnetization, or if a large amplitude of alternating biasmagnetic field is applied, it is necessary to apply a direct excitingfield for exciting the ferromagnetic material and generating an adequateintensity of magnetic field for writing. This direct (not alternating)magnetic field corresponds to the magnetic field generated by a drivecurrent in wiring coils of a magnetic head.

As mentioned above, the present invention provides a method forpreformat writing of a tracking servo signal, address signal, clocksignal or other signals into a magnetic record medium, especially a diskmedium such as a hard disk or a large capacity flexible disk, withsubstantially high productivity and low cost.

The present invention also provides more precise tracking for a highertrack density than in the prior art.

The present invention provides an essential solution for the previouslystated problems in the prior art without sacrificing any importantperformances such as a medium S/N ratio or a head-medium interfaceperformance. Thus, the present invention will be an important technologyfor a magnetic record medium with a high record density of gigabit orderand above in the future.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged plan view showing an example of a surface of amaster information carrier according to the present invention;

FIG. 2 shows an example of the master information carrier according tothe present invention in a cross section along a track;

FIG. 3 shows another example of the master information carrier accordingto the present invention in a cross section along a track;

FIG. 4 shows yet another example of the master information carrieraccording to the present invention in a cross section along a track;

FIG. 5 shows yet another example of the master information carrieraccording to the present invention in a cross section along a track;

FIG. 6(a) shows a method for writing master information into a magneticrecord medium using a master information carrier according to thepresent invention;

FIG. 6(b) shows an example of a record magnetization pattern writteninto the magnetic record medium by the method shown in FIG. 6(a);

FIG. 6(c) shows an example of a read signal from the magnetizationpattern written into the magnetic record medium;

FIG. 7 shows another method for writing master information into amagnetic record medium using a master information carrier according tothe present invention;

FIG. 8 shows yet another method for writing master information into amagnetic record medium using a master information carrier according tothe present invention;

FIG. 9(a) shows another method for writing master information into amagnetic record medium using a master information carrier according tothe present invention;

FIG. 9(b) shows an example of a magnetization pattern written into themagnetic record medium;

FIG. 9(c) shows an example of a read signal from the magnetizationpattern shown in FIG. 9(b);

FIG. 10 shows an example of a cross section of the protruding portion ofthe master information carrier according to the present invention alongthe direction of bit length;

FIG. 11 shows another example of a cross section of the protrudingportion of the master information carrier according to the presentinvention along the direction of bit length;

FIG. 12 shows an example of a process for making the master informationcarrier according to the present invention;

FIG. 13 shows another example of a process for making the masterinformation carrier according to the present invention;

FIG. 14 shows yet another example of a process for making the masterinformation carrier according to the present invention;

FIG. 15 is a plan view of an example of a master information carrieraccording to the present invention;

FIG. 16 is a partial cross section showing an apparatus for writinginformation signal of the master information carrier shown in FIG. 15into a magnetic record medium;

FIG. 17(a) is a perspective view showing a method for writinginformation signal of the master information carrier into a magneticrecord medium using the apparatus shown in FIG. 16;

FIG. 17(b) is a perspective view showing another method for writinginformation signal of the master information carrier into a magneticrecord medium using the apparatus shown in FIG. 16;

FIG. 18 is a perspective view showing an example of a method forpre-magnetizing the magnetic record medium;

FIG. 19(a) is a plan view of a master information carrier according tothe present invention;

FIG. 19(b) show a surface contour of the master information carriershown in FIG. 19(a) along the line C-C′;

FIG. 20 is a partial cross section showing an apparatus for writinginformation signal of the master information carrier shown in FIG. 19into a magnetic record medium; and

FIG. 21 is a perspective view showing a method for writing informationsignal of the master information carrier into a magnetic record mediumusing the apparatus shown in FIG. 20.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Below, the preferred embodiments of the present invention are explainedin detail with reference to the accompanying drawings.

(First Embodiment)

The following explanation concerns a basic configuration of the masterinformation carrier according to the present invention and the methodfor writing the master information signal into a magnetic record mediumusing the master information carrier.

FIG. 1 shows an example of a surface of a master information carrieraccording to the present invention. FIG. 1 shows a master informationpattern to be written in a preformat area that is disposed at a givenpredetermined angular distance along circumferential direction (i.e. thetrack direction) for ten tracks in radial direction (i.e. in thedirection traversing the track) of the disk. In FIG. 1, areas defined bybroken lines correspond to tracks to be used as data areas in themagnetic record medium after writing the master information signal. In areal master information carrier surface, such master informationpatterns as shown in FIG. 1 are formed at a predetermined angulardistance in circumferential direction and in all tracks over the wholerecording area of the magnetic record disk in radial direction.

The master information pattern comprises a tracking servo signal area, aclock signal area and address signal area that are disposed sequentiallyalong the track direction as shown e.g. in FIG. 1. The surface of themaster information carrier according to the present invention has anembossed pattern corresponding to this master information pattern. Eachhatched portion in FIG. 1, for example, is a protruding portion whosesurface is made of a ferromagnetic material. It is preferable to use aferromagnetic thin film formed by vapor deposition or a plating methodas the ferromagnetic material. However, a magnetic coating layer thatcontains magnetic particles dispersed in an organic binder, or a bulkmaterial such as sintered material can be used, too.

The fine embossed pattern corresponding to the information signal asshown in FIG. 1 can be formed easily by utilizing a variety of fineprocessing technique such as a master stamper process for an opticaldisk or a semiconductor process. For example, such a process comprisesthe steps of forming a resist film on a ferromagnetic film, patterningby exposure and development with a photolithography technique or alithography technique using laser or electron beams, and dry etching tomake a fine embossed pattern on the ferromagnetic film. Alternatively,it may comprise the steps of patterning a resist film on a substrate,forming a ferromagnetic film, and removing the resist film to make afine embossed pattern by the ferromagnetic film. This process is calledliftoff method. It is possible to make the fine embossed pattern withoutusing a resist film by a direct fine process using a laser, electronbeam, ion beam, or other machining, as long as the fine embossed patterncorresponding to the information signal is formed with a high precision.Some examples of fine processes that are suited for making the masterinformation carrier of the present invention will be explained in detailunder the Second Embodiment.

FIGS. 2-4 show examples of a cross section of the master informationcarrier shown in FIG. 1 along phantom line A—A′. FIGS. 2 and 3 showexamples whose embossed pattern corresponding to the master informationis formed after forming ferromagnetic film 22, 32 on planar substrate21, 31. The ferromagnetic film 22 in FIG. 2 remains at the bottomportion as well as the protruding portion of the embossed pattern. Onthe other hand, the ferromagnetic film 32 in FIG. 3 remains only at theprotruding portion of the embossed pattern as the bottom portion is inthe substrate 31. Both examples are acceptable.

In the example of FIG. 4, ferromagnetic film 42 is formed after makingan embossed pattern in the surface of the substrate 41. This example mayhave a disadvantage in that edges of the surface of the ferromagneticfilm 42 at the protruding portion have a tendency to be round, so asharp step may not be obtained. In this case, during the writing ofmaster information on the magnetic disk medium, the gradient of themagnetic field at a boundary between the protruding portion and thebottom portion may be decreased and deterioration of writing performancemay occur.

On the other hand, the configuration of FIG. 2 or 3 is generallypreferable compared with that of FIG. 4 since the magnetic field forwriting may have a sufficiently large gradient at the boundary betweenthe protruding portion and the bottom portion. However, it is necessaryto be careful so that a resist layer or deteriorated layer is completelyremoved from the surface of the ferromagnetic film after making theembossed pattern. Otherwise, the remaining substances may cause spacingloss in the writing process of master information onto the magnetic diskmedium.

Concerning the material of the substrate, there is no limitation as longas the ferromagnetic film can be formed on the substrate and the fineembossed pattern can be processed precisely corresponding to the masterinformation signal. However, it is better to use a material whosesurface-roughness is small and which has excellent flatness. If thesurface of the substrate is rough, the surface of the ferromagnetic filmformed on the substrate may be rough too, and a write-spacing loss mayincrease when writing the master information into the magnetic disk. Asa material having a small surface-roughness, a variety of glasses usedfor magnetic disks or optical disks, polymeric material such as apolycarbonate, metals such as Al, Si substrates, or carbon can be used.

Concerning the above mentioned write-spacing loss, it is preferable thatthe surface of the master information carrier and the surface of themagnetic disk contact with each other securely when the masterinformation is written into the magnetic disk. Especially if themagnetic record disk into which the master information is written is ahard disk, the surface of the master information carrier preferably isable to compensate a fine wimple or bending of the hard disk to realizea secure contact state over the whole disk surface. Therefore, amaterial having some flexibility, for example a sheet or disk made ofpolymer or thin metal is preferable as the substrate material for themaster information carrier. From this viewpoint, an example of themaster information carrier having a preferred substrate will beexplained later in Third Embodiment.

A depth of the bottom of the embossed pattern, that is the distancebetween the surface of the protruding portion and the bottom, is usuallyset at more than 0.05 microns, preferably more than 0.1 microns, thoughit depends on the surface condition of the magnetic disk medium in whichthe master information is written or the bit size of the masterinformation. If the ferromagnetic material remains at the bottom of theembossed pattern as shown in FIG. 2 or 4, the depth of the bottom below0.1 microns may result in an insufficient gradient of the magnetic fieldfor writing. The depth of the bottom above 0.1 microns is preferablealso for maintaining the secure contact state between the surface of themaster information carrier and the surface of the magnetic disk when themaster information is written onto the magnetic disk.

The ferromagnetic film can be formed by a usual method for forming athin film, such as sputtering, vacuum vapor deposition, plating, orchemical vapor deposition (CVD).

A variety of materials can be used for forming the ferromagnetic film,such as a hard magnetic material, semihard magnetic material or softmagnetic material as explained previously. However, it is better thatthe saturation magnetic flux density of the material is large togenerate a sufficient magnetic field for writing regardless of a kind ofthe magnetic disk into which the master information is written.Especially, when writing into a disk with a high coercive force above150 kA/m or a flexible disk with a thicker magnetic layer, a materialwith a saturation magnetic flux density above 0.8 T, preferably above1.0 T, is used generally. Otherwise the writing cannot be performedsufficiently.

Furthermore, the thickness of the ferromagnetic film also influences thewriting ability into the magnetic disk. A certain thickness of theferromagnetic film is necessary to generate a sufficient magnetic fieldfor writing regardless of a kind of the magnetic disk, though, on theother hand, the influence of a demagnetizing field due to the bit shapeof the master information should be taken into consideration. In theconfiguration of the present invention, the ferromagnetic film of theprotruding portion of the master information disk is magnetized alongthe track direction in the film plane for generating the magnetic fieldfor writing, except for the special case where the magnetic disk is aperpendicular magnetic record medium or other special cases. However, ifthe thickness of the ferromagnetic film is too large, the writingability is decreased since the leakage flux decreases by the influenceof the demagnetizing field. Therefore, the thickness of theferromagnetic film should be set at an adequate value depending on thebit length of the master information. For example, if the least bitlength of the master information is 1-2 micron, the adequate thicknessof the ferromagnetic film may be 0.1-1.0 micron.

Preferred magnetic characteristics of these ferromagnetic materials willbe explained later together with a method for writing the masterinformation into the magnetic disk.

FIG. 5 shows another example of the cross section of the masterinformation carrier along the phantom line A—A′ in FIG. 1. This examplein FIG. 5 differs from the examples shown in FIGS. 2-4 in that thesubstrate itself is made of the ferromagnetic material. In other words,a film formation step is not necessary in this example since theembossed pattern corresponding to the master information is formed onthe surface of the substrate 51 made of the ferromagnetic material.Thus, the productivity for making the master information carrier isimproved compared to FIGS. 2-4.

If a bulk material such as a sintered material is used for theferromagnetic substrate 51, the surface-roughness of the masterinformation carrier may be large. In this case, the write spacing mayincrease when writing the master information onto the magnetic disk, sothe substrate material chosen should have a surface as smooth aspossible. Generally, a bulk material such as a sintered material doesnot have flexibility, so the example in FIG. 5 is more suitable forwriting into a flexible disk rather than a hard disk.

A method for writing the master information signal into the magneticdisk using the above-mentioned master information carrier is explainedin the following. FIG. 6(a) shows the method for writing the masterinformation into the in-plane magnetic record medium. FIG. 6(b) shows amagnetization pattern that was written into the magnetic record medium.FIG. 6(c) shows an example of a read-back signal of the above writtenmagnetization pattern detected by a magnetoresistive (MR) type head.FIGS. 6(a) and 6(b) are both the cross sections of the magnetic recordmedium along the track direction.

When writing onto the in-plane magnetic record medium, the ferromagneticmaterial that forms the protruding portion of the master informationcarrier 61 is magnetized in the direction 63, along a track parallel tothe surface of the magnetic record medium 62, as shown in FIG. 6A. Thismagnetization 63 is given by residual magnetization generated bypreviously saturating the ferromagnetic material that forms theprotruding portion along the track direction, e.g. if the ferromagneticmaterial of the protruding portions is a highly coercive material.Materials composed of rare earth elements and transition metal materialsuch as Sm—Co or Ne—Fe—B are suitable as highly coercive material forthe above mentioned ferromagnetic material since they have a highcoercive force and high saturation flux density.

The surface of the master information carrier 61 causes a change of themagnetic reluctance due to the embossed pattern. Thus, the magnetization63 of the ferromagnetic material at the protruding portion generates themagnetic field 64 for writing. This magnetic field 64 has oppositepolarities for the surfaces of the protruding portion and the bottom ofthe master information carrier 61. Consequently, the magnetizationpattern 65 shown in FIG. 6(b) is written into the magnetic record medium62, corresponding to the embossed pattern.

The read signal waveform is shown in FIG. 6(c), which is read using amagnetic head and attained from the magnetization 65 recorded by themethod of the present invention. The waveform shown in FIG. 6(c) isbasically similar to that of the signal read from the magnetizationrecorded by the method in the prior art using a magnetic head.Therefore, there is no problem in processing the read signal. Thewriting method of the present invention is rather superior regarding thesymmetry of the read signal to the method using a magnetic head,probably because the method of the present invention is not accompaniedby relative movement of the master information carrier and the magneticrecord medium.

In the writing step according to the present invention, applying analternating and decaying bias magnetic field improves the efficiency ofwriting, as explained before. Considering the technical field of theinvention, it is preferable to utilize a basically digital saturationrecording in the writing process of the present invention. However,there may be some cases with insufficient writing ability depending onthe information signal pattern to be written or the magneticcharacteristics of the magnetic record medium. In these cases, applyingthe alternating and decaying bias magnetic field will be effective meansto obtain a sufficient saturation writing.

A writing mechanism with applying the alternating bias magnetic field isbasically the same as an analog alternating bias writing in the priorart. However, the recording method of the present invention is a staticrecording without relative movement between the master informationcarrier and the magnetic recording medium. Therefore, a frequency of thealternating bias magnetic field is not as limited as the analogalternating bias writing in the prior art. The frequency of thealternating magnetic field to be applied in the method of the presentinvention can be 50 or 60 Hz, as is used for commercial AC power supply.

A decay time of the alternating bias magnetic field is set substantiallylonger than a period of the alternating bias magnetic field, preferablymore than five periods. For example, if the frequency of the alternatingbias magnetic field is 50 or 60 Hz, more than 100 ms may be enough forthe decay time.

On the other hand, the method shown in FIG. 6(a) requires a maximumamplitude of the alternating magnetic field that is less than a coerciveforce of the ferromagnetic material that forms the protruding portion ofthe master information carrier 61. In the method shown in FIG. 6(a),applying an alternating bias magnetic field greater than the coerciveforce of the ferromagnetic material will decrease the magnetization 63of the magnetic material of the protruding portion. In this case, it isdifficult to obtain a sufficient magnetic field 64 for writing.

In the above explanation, a highly coercive material is used for theferromagnetic material that forms the protruding portion of the masterinformation carrier. However, there are some cases where it is difficultto get a sufficient magnetization with an easy magnetization directionset along a track, owing to the embossed pattern formed on the surfaceof the master information carrier when using a highly coercive material.

For example, if a bit shape of the master information signal iselongated in the direction across the tracks, the ferromagnetic materialthat forms the protruding portion of the master information carrier isinfluenced by shape anisotropy in the direction across tracks so thatthe direction across the tracks tends to be an easy axis. In this case,the residual magnetization generated by saturating the ferromagneticmaterial along the track is too small to obtain a magnetic field alongthe track for writing. In addition, a hard magnetic highly coercivematerial usually has difficulty in controlling magnetic anisotropy.Therefore, it is difficult to induce the anisotropy that is enough tocompensate the contribution of the above mentioned bit shape, in thedirection along the track.

To solve the above-mentioned problem, it is preferable to make theferromagnetic material that forms the protruding portion of the masterinformation carrier using a soft magnetic material or a hard or semihardmagnetic material having lower coercive force. There is no specificboundary between a hard magnetic material and a semihard magneticmaterial. In this specification, the term “semihard magnetic material”is used as a generic term for hard or semihard magnetic materials havinga small coercive force (below 60 kA/m for example), that is less than ahalf value of a usual magnetic record medium (120-200 kA/m).

Such a soft or semihard magnetic material can be treated easily to havean adequate anisotropy by adding a variety of energies in the process ofmaking the material or annealing the material in the magnetic field,compared with a hard magnetic material having a highly coercive force.Therefore, the above mentioned anisotropy due to the bit shape may becompensated easily, too. Furthermore, many soft or semihard materialshave a large saturation flux density suitable for the ferromagneticmaterial that forms the protruding portion of the master informationcarrier. As the soft magnetic material suitable for the ferromagneticmaterial that forms the protruding portion of the master informationcarrier of the present invention there are, for example, a crystallinematerial such as Ni—Fe or Fe—Al—Si, an amorphous material of the Cogroup such as Co—Zr—Nb, or an Fe microcrystalline material such asFe—Ta—N. For the semihard magnetic material having a low coercive force,for example, Fe, Co, Fe—Co and other materials are suitable.

Though the ferromagnetic material that forms the protruding portion ofthe master information carrier in the present invention should bemagnetized in one direction to generate a magnetic field for writing ina writing process, a soft magnetic material or a semihard magneticmaterial usually does not provide a stable one-direction magnetizationin a residual magnetization state. Therefore, in many cases, a directexciting field is applied for exciting the material to generate anadequate magnetic field for writing. As mentioned before, this directexciting field corresponds to a magnetic field generated by a currentthat flows in coil windings of the magnetic head.

FIG. 7 shows the method for writing the master information signal usinga direct magnetizing field as mentioned above. FIG. 7 is also the crosssection along the track of the magnetic record medium similar to FIG.6(a).

The soft magnetic material or the semihard magnetic material that formsthe protruding portion of the master information carrier is magnetizedby the direct exciting field 75 in the direction along the track of themagnetic record medium 72 to generate the magnetic write field 74. Thedirect exciting field 75 cannot be so strong since it is applied to themagnetic record medium 72, too. The intensity of the direct excitingfield 75 is preferably as large as, or below the coercive force of themagnetic record medium in most cases. If the intensity of the directexciting field 75 is as large as, or less than the coercive force of themagnetic record medium, the magnetic field for writing 74 generated bythe soft magnetic material or the semihard magnetic material of theprotruding portion is much stronger than the intensity of the directexciting field. Thus, the magnetization pattern can be writtencorresponding to the embossed pattern, in the same manner as shown inFIG. 6(b). The adequate intensity of the direct exciting field 75 can bevaried due to the magnetic characteristics of the soft or semihardmagnetic material that forms the protruding portion of the masterinformation carrier, magnetic characteristics of the magnetic recordmedium, embossed pattern shape, or other factors. Therefore, theintensity of the direct exciting field should be optimizedexperimentally to obtain the most adequate writing characteristics ineach case.

From the above viewpoint, the soft or semihard magnetic material thatforms the protruding portion of the master information carrierpreferably reaches substantial saturation by the direct exciting field75 whose intensity is as large as, or below the coercive force of themagnetic record medium. Most soft magnetic materials show goodsaturation characteristics in a small magnetic field. However, somesemihard magnetic materials need a large magnetic field for saturation,so attention should be paid when selecting the material. Material havinga coercive force below 40 kA/m is preferable as the semihard magneticmaterial when writing into a hard disk having a usual coercive force ora large-capacity flexible disk. If the coercive force is more than 40kA/m, an intensity of the direct exciting field 75 that is significantlylarger than the coercive force of the magnetic record medium isnecessary for stable magnetization of the semihard magnetic materialalong the track of the magnetic record medium 72. Thus, it is difficultto write with a precise resolution in some cases.

The writing method with applying the direct exciting field as shown inFIG. 7 is effective also in the case where the ferromagnetic materialthat forms the protruding portion of the master information carrier hasa large coercive force, especially when applying an alternating biasmagnetic field whose intensity is larger than the coercive force. Asmentioned above, if an alternating bias magnetic field that is largerthan the coercive force of the ferromagnetic material is applied in FIG.6, the magnetization 63 of the ferromagnetic material that forms theprotruding portion decreases, so that a sufficient magnetic field forwriting 64 cannot be obtained. In this case, by superposing the directexciting field on the alternating bias magnetic field, the totalexternal magnetic field that is applied in the opposite direction tomagnetization 63 of the ferromagnetic material decreases, so that thestable magnetic field for writing can be generated similarly to the casewhere the alternating bias magnetic field is not applied. Application ofthe alternating and decaying bias magnetic field superposed on thedirect exciting field as mentioned above is also effective for the casewhere the ferromagnetic material that forms the protruding portion ofthe master information carrier is a semihard or soft magnetic material.

In some cases depending on the embossed pattern on the surface of themaster information carrier, a better written state can be obtained byerasing the magnetic record medium previously with a direct saturationand giving an initial magnetization 86 in one direction as shown in FIG.8.

The embossed pattern can be a variety of patterns depending on theinformation signal required for each application. Therefore, in someembossed pattern, either the magnetic field on the surface of theprotruding portion site or the magnetic field on the bottom portion siteis much weaker than the other. Thus, the weaker magnetic field cannotperform saturation writing, or the linearity of writing is deteriorated.In FIG. 8, it is preferable to erase the magnetic record medium 82previously by a direct saturation in the direction of the weakermagnetic field, which is either the magnetic field 84 a on the surfaceof the protruding portion site or the magnetic field 84 b on the bottomportion site, to promote the saturation writing in this direction.

In FIG. 8, the magnetic record medium 82 is previously erased with thedirect saturation magnetization in the opposite direction to themagnetization 83 of the ferromagnetic material that forms the protrudingportion. However, it is clear from the above explanation that thepolarity for erasing a magnetic record medium by the direct saturationdepends on the case. For example, in some cases, a better resolution forwriting is obtained by erasing the magnetic record medium 82 using adirect saturation in the same direction as the magnetization 83 of theferromagnetic material at the protruding portion of the masterinformation. Though the direct exciting field 85 is applied in theconfiguration shown in FIG. 8 in the same manner as shown in FIG. 7, theeffect of previously erasing with a direct exciting field is obtainedeven if the direct exciting field 85 is not applied.

The above explanation concerns writing into in-plane magnetic recordmedia. However, the writing method of this invention can be utilized forvarious magnetic recording media in a variety of embodiments to obtainsimilar effects.

A typical variation of the writing method according to the presentinvention is shown in FIG. 9 where the master information is writteninto a perpendicular magnetic record medium. FIG. 9(a) shows the writingmethod of the master information signal into the perpendicular magneticrecord medium using a master information carrier. FIG. 9(b) shows amagnetization pattern written into the perpendicular magnetic recordmedium. FIG. 9(c) shows an example of the waveform of a read signal readby a magnetoresistive (MR) type head from the magnetization pattern.FIGS. 9(a) and 9(b) are cross sections along the track direction of themagnetic record medium similar to FIGS. 6-8.

When writing into the perpendicular magnetic medium, magnetization 93 isapplied to the ferromagnetic material of the protruding portion of themaster information carrier 91 in the direction perpendicular to thesurface of the magnetic record medium 92. Therefore, if theferromagnetic material of the protruding portion is a ferromagneticfilm, a thickness of the film should be large enough for reducing ademagnetization field in the direction perpendicular to the surface.

If the direct exciting field 95 is applied, its direction should beperpendicular to the surface of the magnetic record medium 92,differently from the in-plane writing. The previous erasing of themagnetic record medium 92 with direct saturation is performed also inthe direction perpendicular to the surface of the magnetic record medium92 so that the initial magnetization 96 can remain in the verticaldirection.

(Second Embodiment)

This second embodiment will explain an example of the master informationcarrier having superior record resolution uniformly over the large area,and an example of the process for making the master information carrierefficiently at a low cost.

In the above mentioned first embodiment, the surface of the masterinformation carrier shown in FIGS. 1-5 should be processed to make afine embossed pattern corresponding to the information signal to bewritten for preformat, using photolithography or other techniques.However, depending on the process for making the master informationcarrier, it is sometimes difficult to form an embossed patterncorresponding to the information signal with a sufficient resolution,when forming the embossed pattern with a high record density in which abit length is below several microns. Especially, if the masterinformation disk is to be used for writing into a disk with largediameter such as 3.5 or 5 inches, usual photolithography process cannotprovide a uniform accuracy over such a large area, so the embossedpattern may have some microscopic difference depending on its location.

For example, the master information carrier having a cross section shownin FIG. 3 was made by steps of forming a ferromagnetic film 32 on thesurface of the planar substrate 31, coating a resist film on thesurface, exposing and developing the resist film to form the patterncorresponding to the digital information signal, and forming the fineembossed pattern on the surface of the ferromagnetic film by a dryetching technique such as an ion milling.

Though the section profile of the protruding portion is simplified witha rectangular shape in FIG. 3, it is difficult to form such arectangular section over a large area in a real master informationcarrier made using regular photolithography. The section profile of theprotruding portion usually assumes a trapezoidal shape, where the lengthof the upper side differs from the length of the lower side, not arectangular shape. In addition, the edges of the upper side at thesurface of the trapezoid become rounded in general.

Such a section profile results primarily from the fact that theresolution of the exposing or developing process of the resist film isnot sufficient for the bit length of the digital information signal. Thesection profile of the patterned resist film has already been atrapezoid and its edges at the upper side have already been rounded.Thus, the section profile of the protruding portion of the ferromagneticfilm that is formed by the dry etching technique such as the ion millingbecomes a rounded trapezoid, inheriting the section profile of thepatterned resist film.

Furthermore, the above mentioned section profile cannot be uniform overa large area, so some microscopic differences of the section profile maybe observed depending on the location, in spite of having the samepatterning. Such a microscopic difference of the section profile of theembossed pattern may undesirably influence the S/N ratio of the signalwritten for the preformat.

The above problem can be solved by using an advanced photolithographytechnique that can realize sufficient accuracy and resolution over thelarge area. However, in this case, even if the above problems aresolved, a substantially expensive exposing machine, resist material,developing liquid and other things are necessary. Consequently, theproductivity of the master information carrier may drop and the cost formaking the master information carrier may rise.

On the contrary, this embodiment can control the variation of the S/Nratio due to the variation of the section profile within a certaintolerance by improving the section profile of the embossed pattern evenif an inexpensive photolithography process is used.

The inventors have searched for a preferred section profile of theembossed pattern that has little influence on the S/N ratio of thesignal. As a result, it was found that a first or second configurationof the protruding portion of the master information carrier explainedbelow can control the variation of the S/N ratio within a certaintolerance.

FIG. 10 shows a first configuration of the protruding portion. In thisconfiguration, the section profile of the protruding portion along thebit length direction of the digital information signal is substantiallya trapezoid with an upper side at the surface and a lower side on thesubstrate. The upper side length “a” is less than the lower side length“b”, and the difference (b−a) between the both side lengths is less thantwice the height of the trapezoid. Such a section profile of theprotruding portion can control the variation of the S/N ratio due to themicroscopic variation of the section profile within a certain tolerance,even when writing a digital information signal for the preformat, withseveral microns bit-length.

The S/N ratio of the read signal is influenced not only by the intensityof the magnetic field for preformat writing generated from theferromagnetic film 102 at the protruding portion of the masterinformation carrier, but also the gradient of the magnetic field at theboundary between the protruding portion and the bottom, i.e., at theedges of the upper side of the protruding portion. If the differencebetween the upper side length “a” and the lower side length “b” of thetrapezoid section of the protruding portion is less than twice of theheight “h” of the trapezoid, the gradient of the magnetic field israther steep. Therefore, it could be established that the S/N ratio ofthe read signal is large and the variation of the S/N ratio due to themicroscopic variation of the section profile is small under the abovecondition.

On the contrary, if the difference between the upper side length “a” andthe lower side length “b” is more than twice of the height “h” of thetrapezoid, leakage from slant faces decreases the gradient of themagnetic field at the edges of the upper side. Therefore, the variationof the S/N ratio of the read signal due to the variation of the sectionprofile increases beyond a certain tolerance, so that a uniform andsufficient S/N ratio of the read signal cannot be obtained over a largearea.

If the bit length of the digital information signal to be written isless than one micron, field gradient variation due to the microscopicshape variation at the edges of the upper side can influence the S/Nratio of the read signal. In this case, curvature radii r, r′ at edgesof the upper side are preferably set below a half of the upper sidelength. Thus, the variation of the S/N ratio due to the microscopicvariation of the section profile is controlled within a tolerance, evenwhen a digital signal with a bit length of less than 1 μm is recorded.

As mentioned above, the first configuration permits the section profileof the protruding portion to have a trapezoid shape, so the embossedpattern can be formed by a regular, widely used photolithographyprocess, without having to use an advanced photolithography technique.Therefore, the master information carrier having the first configurationcan be produced efficiently at low cost.

As explained in the first embodiment, the thickness of the ferromagneticfilm may influence the S/N ratio of the read signal when performingpreformat writing by use of the above mentioned master informationcarrier. If the thickness of the ferromagnetic film 102 in FIG. 10 istoo thin, a sufficient magnetic field cannot be generated for writing,and the gradient of the magnetic field may decrease at the boundary ofthe protruding portion and the bottom portion. Thus, it is difficult toperform sufficient writing.

On the other hand, when writing a preformat signal into an in-planemagnetic record medium, if the thickness of the ferromagnetic film 102is too thick, the demagnetizing field due to the profile of theprotruding portion makes it difficult to generate a sufficient magneticfield. For example, preformat writing into the in-plane magnetic disk isperformed by applying a direct exciting field along the circumferentialdirection in the disk plane for magnetizing the ferromagnetic film 102at the protruding portion of the master information carrier, and thedigital information signal corresponding to the embossed pattern iswritten. However, if the upper side length “a” of the protruding portioncorresponding to the bit length of the signal is not sufficiently largerthan the thickness of the ferromagnetic film 102, the demagnetizingfield in the opposite direction to the magnetization of theferromagnetic film 102 increases, so that the magnetic field for writinggenerated by the protruding portion is weakened.

The influence of the above mentioned demagnetizing field causes a dropof the S/N ratio if the thickness of the ferromagnetic film 102 islarger than a half of the upper side length “a” of the protrudingportion. However, the drop of the S/N ratio is small enough to beneglected if the thickness of the ferromagnetic film 102 is smaller thana half of the upper side length “a” of the protruding portion.Therefore, it is preferable to ensure that the thickness of theferromagnetic film 102 can generate a sufficient magnetic field forwriting in a thickness region below one half of the upper side length“a”, especially in a master information carrier with in-plane preformatwriting.

On the other hand, when writing the preformat signal into aperpendicular magnetic record medium, a direct exciting field is appliedin the direction perpendicular to the ferromagnetic film 102 tomagnetize the ferromagnetic film 102, and a digital information signalis written corresponding to the embossed pattern. In this case,differently from the case with in-plane writing, the magnetic field forwriting is dropped due to the demagnetizing field, the more theferromagnetic film becomes thinner. Therefore, a master informationcarrier to be used for preformat writing into the perpendicular magneticrecord medium should have a thickness of the ferromagnetic film 102 thatis larger than the upper side length “a”, preferably more than twice theupper side length “a” of the protruding portion of the ferromagneticfilm 102.

FIG. 11 shows a second configuration of the protruding portion. In thisconfiguration, the section profile of the protruding portion along thedirection of the bit length of the digital information signal issubstantially a trapezoid with an upper side at the surface and a lowerside on the substrate, and the upper side length “a” is larger than thelower side length “b”. This upside-down trapezoid section of theprotruding portion can obtain a sufficient S/N ratio of the read signaland control the variation of the S/N ratio within a tolerance over alarge area, in spite of some microscopic variation of the sectionprofile, even when a digital signal with a bit length of less than 1 μmis recorded.

As previously mentioned, the S/N ratio of the read signal is influencedby the intensity of the magnetic field for preformat writing generatedfrom the ferromagnetic film at the protruding portion of the masterinformation carrier, and by the gradient of the magnetic field at theboundary between the protruding portion and the bottom portion, that isthe edges of the upper side of the protruding portion. In the secondconfiguration, the angles between the upper side and slant faces areacute angles since the upper side length “a” is larger than the lowerside length “b” of the trapezoid section of the protruding portion. Sucha configuration reduces the influence of the leakage magnetic fieldgenerated by the slant faces and provides a steep gradient of themagnetic field at the edges of the upper side, so that a sufficient S/Nratio of the read signal is obtained.

Furthermore, the difference between the upper side length “a” and thelower side length “b” as well as the gradient variation of the magneticfield at each edge of the upper side is small in the secondconfiguration. As a result, the variation of the S/N ratio of the readsignal due to the microscopic variation of the section profile also canbe within a tolerance. Therefore, as in the first embodiment, a uniformand sufficient S/N ratio of the read signal over a large area can beobtained.

The thickness of the ferromagnetic film 112 influences the S/N ratio ofthe read signal in the second configuration, too. The standard fordetermining the thickness of the ferromagnetic film 112 is the same asthat mentioned in the first configuration. The thickness of theferromagnetic film 112 is preferably less than a half of the upper sidelength “a” for the master information carrier for an in-plane magneticrecord medium, and is preferably more than twice the upper side length“a” for the master information carrier for a perpendicular magneticrecord medium.

The master information carrier having the second configuration can bemanufactured by a photolithography technique using, for example, aliftoff process. The following explains an example of a process suitablefor making a master information carrier having the second configuration.

FIG. 12 shows an example of the process for making the masterinformation carrier according to the second configuration.

First, as shown FIG. 12(a), the embossed pattern corresponding to thedigital information signal is formed on the substrate 121 with thephotoresist film 123. The cross section in the bit-length direction ofthe protruding portion formed by the photoresist film 123 issubstantially trapezoidal with an upper side at the surface and a lowerside on the substrate, and the upper side length is shorter than thelower side, as shown in FIG. 12(a).

Then, as shown in FIG. 12(b), the ferromagnetic film 122 is formed onthe substrate 121 and the protruding portion formed by the photoresistfilm 123. A usual method such as a vacuum vapor deposition, sputteringor plating can be used for forming the ferromagnetic film 122.

Then, as shown in FIG. 12(c), the surface of the ferromagnetic film 122is etched a little by ion milling or another method. After that, thephotoresist film 123 and the ferromagnetic film 122 formed on thephotoresist film 123 are removed by a liftoff method. Thus, as shown inFIG. 12(d), the master information carrier is made, which includes thesubstrate 121 and the protruding portion of the ferromagnetic film 122formed on the substrate 121, and the section profile of the protrudingportion is a trapezoid with an upper side longer than a lower side. Theliftoff process is performed by melting the photoresist film 123 byusing a special solvent called “remover”, for removing the ferromagneticfilm 122 formed on the photoresist film 123 together with thephotoresist film 123.

The etching step of the ferromagnetic film surface shown in FIG. 12(c)is performed for making the liftoff easy by removing the ferromagneticfilm 122 deposited on the slant faces of the protruding portion formedwith the photoresist film. This step can be eliminated if the thicknessof the ferromagnetic film 122 is thin. In this case, however, theaccuracy of patterning of the ferromagnetic film 122 after the liftoffmay be deteriorated and ferromagnetic film or photoresist film 123 canremain partially. Therefore, it is better not to eliminate the etchingstep shown in FIG. 12(c).

In the etching step shown in FIG. 12(c), ion milling for etching theferromagnetic film can be replaced with a vacuum dry process such assputter etching or a wet process such as chemical etching.

If a vacuum dry process such as sputtering or ion milling is used forthis etching step, it is preferable to irradiate the ion 124 from theslant direction against the surface of the substrate 121 since thisetching process is performed for making the liftoff easy by removing theferromagnetic film 122 deposited on the slant faces of the protrudingportion formed with the photoresist film 123. According to experiments,it was found that the ferromagnetic film 122 deposited on the slantfaces can be removed effectively when an incident angle of the ion 124with respect to the normal of the substrate 121 is more than 20 degrees.

FIG. 13 shows another example of the process for making the masterinformation carrier having the second configuration.

First, as shown in FIG. 13(a), a conductive film 134 is formed on thesubstrate 131. Then, an embossed pattern corresponding to the digitalinformation signal is formed on the conductive film 134 using aphotoresist film 133, as shown in FIG. 13(b). The section profile of theprotruding portion formed with the photoresist film 133 is a trapezoidwith an upper side at the surface that is longer than a lower side onthe substrate as shown in FIG. 13(b).

Then, as shown in FIG. 13(c), a ferromagnetic film 132 is formed on theconductive film 134 and the protruding portion of the photoresist film133 with an electroplating method.

Then, the photoresist film 133 is removed. Thus, as shown in FIG. 13(d),the master information carrier is completed, which includes a conductivefilm 134 and a protruding portion of the ferromagnetic film 132 whosesection profile is a trapezoid with an upper side longer than a lowerside. The photoresist film 133 is removed by melting the photoresistfilm 133 by a solvent called “remover” in the same way as shown in FIG.12(d).

Differently from the process shown in FIG. 12, this process shown inFIG. 13 forms the ferromagnetic film 132 by electroplating, so theferromagnetic material does not deposit on the surface of the protrudingportion of the photoresist film 133. Therefore, the photoresist film 133can be removed easier than in the process shown in FIG. 12. In addition,an etching step of the ferromagnetic film 132 is not required in thisprocess. The step for forming the conductive film 134, which is requiredin this process shown in FIG. 13, can be eliminated by using a substrate131 made of a conductive material.

Though the material and thickness of the conductive film 134 are notlimited, it is preferable to obtain a film with a smallsurface-roughness. If the surface-roughness of the conductive film 134is large, the surface-roughness of the ferromagnetic film 133 formedthereon may also become large, and the surface-roughness can influence adistribution of the magnetic field for preformat writing. Therefore, itis desirable to select the continuous thin film material with littlesurface roughness and as thin as possible, as long as a sufficientconductivity for electroplating can be obtained.

If the reflectivity of the surface of the conductive film 134 is largeat a wavelength region of light for exposing the photoresist film, theresolution at exposure can be deteriorated due to the influence of thereflecting light. Therefore, it is desirable to use a material for theconductive film whose reflectivity at the surface is small, preferablyless than 50% at a wavelength of light for exposing the photoresist film133.

As mentioned above, the resolution at exposing the photoresist film canbe improved when the conductive film 134 has a function ofanti-reflection coating compared with the case where the patterning ofthe resist film is performed directly on the substrate 131. Thisconductive film 134 with anti-reflection function can be a conductivecarbon film or a film with some impurities containing a carbon as a maincomponent, for example.

It is also preferable when selecting a material for the conductive filmto consider a compatibility of the material with the ferromagneticmaterial to be disposed on the conductive film 134. Deposition rate,construction or magnetic characteristics of the ferromagnetic film 132formed on the conductive film by electroplating may change depending onthe material of the conductive film. Therefore, it is preferable toselect the most proper conductive film material considering theferromagnetic film material to be used.

If the substrate material is selected from conductive material, it ispreferable to pay the same attention as mentioned above concerning theconductive film.

In the example of the process for making a master information carrierhaving the second configuration mentioned above, the section profile ofthe protruding portion of the photoresist film 133 is permitted to be atrapezoid. Therefore, a regular, widely used photolithography processcan be used without using a special advanced photolithography technique.Thus, the master information carrier can be produced efficiently at lowcost in the same way as the master information having the firstconfiguration explained previously.

(Third Embodiment)

It is necessary that the surface of the master information carrier andthe surface of the magnetic record medium keep a uniform and securecontact when writing a master information into the magnetic recordmedium. If secure and uniform contact is not kept between the twosurfaces, the master information signal can be written incorrectly intothe magnetic record medium due to spacing loss. In this case, the readsignal from the medium may include a partial lack of data ordeteriorated S/N ratio.

This embodiment provides a suitable configuration of the masterinformation carrier for maintaining a secure and uniform contact betweenthe surface of the master information carrier and the surface of themagnetic record medium, a master information carrier that can performpreformat writing with high reliability, as well as a method forproducing the master information carrier.

If the magnetic record medium into which the master information ispreformat-written is a hard disk, its substrate is a hard material suchas metal, glass, silicon or carbon. Therefore, it is preferable that thesubstrate of the master information carrier has flexibility to a certainextent so that the surface of the master information carrier cancompensate a fine wimple or bending to keep a secure contact state overthe whole disk surface. A polymer material is suitable for making such asubstrate of the master information carrier.

The master information carrier of the present invention can keep asecure and uniform contact with the surface of the hard disk thatincludes a hard substrate and a magnetic film formed on the substrate,by using a polymer material for the substrate of the master informationcarrier. Thus, the master information carrier of the present inventioncan raise the reliability of the preformat writing.

However, for preformat recordings of harddisks having a future arealrecording density in the 10-gigabit-order, substantial improvement wasfound to be necessary in environmental resistance properties or handlingproperties when using a polymer material that is soft compared to thehard disk substrate for the substrate of the master information carrier.For example, dimension stability against an expansion or contraction dueto a change of temperature or humidity, a physical and chemicalstability in the process for making the master information carrier, anda processability of the material should be raised. In addition, toensure a secure and uniform contact between the surface of the masterinformation carrier and the surface of the magnetic record medium, anelectrostatic sticking of dust should be suppressed.

The inventors have studied the structure of master information carriershaving a substrate that includes a polymer material. As a result, it wasfound that the above mentioned problems are solved by using a masterinformation carrier having a structure as explained below.

First, a structure for improving the environmental resistance propertyis explained. A substantially high accuracy of dimensions should berequired of the substrate of the master information carrier to writepreformat data into a hard disk having an areal recording density of10-giga-bit order in the future. Furthermore, this high accuracy shouldbe realized in various circumstances such as manufacturing process,preformat-writing step, and storing of the master information carrier.There is no material that can satisfy such a request for theenvironmental resistance by itself alone.

For example, polyimide and polyamide resins have excellent stabilityagainst heat and chemicals, but they have a tendency to expand due towater absorption. The tendency of polyethylenetherephtalate resins toabsorb water and expand is relatively small, but heat stability is aproblem.

Polypropylene or Teflon (trademark of polytetrafluorethylene) resinshave excellent stability of dimension under various circumstances, butthey have weak adhesiveness with the ferromagnetic film.

The substrate of the master information carrier according to the presentinvention has a multi-layer construction of at least two of the polymermaterials having different properties as mentioned above. Thus, theadvantages of each material are utilized and disadvantages of eachmaterial are compensated.

As one of the preferable examples, the substrate of the masterinformation carrier has a multi-layer construction of a polypropylene orTeflon resin and a polyimide or a polyamide resin. This masterinformation carrier can maintain an excellent dimension stability undera variety of circumstances, owing to the properties of the polypropyleneor Teflon resin, while it has sufficient adhesiveness with theferromagnetic film that is formed on the surface of the polyimide orpolyamide resin.

The appropriate combination of polymer material and thickness of eachlayer for such a multi-layer construction can be changed depending onthe thermal history in the process for making the master informationcarrier, temperature and humidity when writing preformat data,temperature and humidity when storing the master information carrier andother conditions. It is necessary to select the most suitablecombination and thickness ratio of layers in accordance with eachcondition.

Second, a structure for improving the processability is explained. It issometimes necessary to process the master information carrier into aproper shape in accordance with a shape of the magnetic record mediumafter forming the embossed pattern corresponding to the masterinformation. For example, the master information carrier that is usedfor writing preformat master information into a hard disk preferably hasa proper dimension corresponding to a certain diameter of the hard disk,so that it can be easily handled for preformat writing.

However, a master information carrier having a substrate made of apolymer material usually has a bad processability. Especially, plasticor other deformation sometimes occurs in the process, and deteriorationof dimension accuracy may occur due to the deformation.

The master information carrier of the present invention has a substrateincluding a base made of a metal, alloy or ceramic material; and apolymer material layer formed on the surface of the base. Theprocessability of the whole master information carrier is improved andplastic deformation hardly occurs in the polymer material layer formedon the surface of the base, resulting from the excellent processabilityof the relatively hard base. In addition, a macroscopic stability inshape and handling properties of the master information carrier areraised as a result of the excellent processability of the hard base.

It is difficult for the hard base to meet a fine wimple or bending ofthe magnetic record medium. However, the flexible polymer material layerformed on the surface of the substrate can compensate a fine wimple orbending of the magnetic record medium to ensure secure and uniformcontact state between the protruding portion of the ferromagnetic filmof the master information carrier and the surface of the magnetic recordmedium.

Furthermore, when the master information carrier comprises a base madeof a metal alloy or ceramic material and a polymer material layer formedon the surface of the base, the effect of dimension accuracy concerningenvironmental resistance can be improved, too.

The polymer material layer can be formed on the surface of the base by avariety of methods such as sticking, coating or flowing of monomer orpolymer precursor followed by polymerization after the coating orflowing, or vacuum vapor deposition of the polymer material.

FIG. 14 illustrates an example of the process for making the masterinformation carrier having the above-mentioned structure.

First, a polyimide solution (Torayneece: trademark of Toray IndustryInc.) is diluted with cyclohexanol into a predetermined concentration,and is coated onto the surface of the glass base 141 by using aspin-coater. Then, it is cured at high temperature to obtain thesubstrate comprising the glass base 141 and the polyimide layer 142formed on the glass base 141, as shown in FIG. 14(a). The thickness ofthe polyimide layer 142 should be optimized depending on the conditionof the application. In one example, it was approximately 1.0 micronafter curing.

Then, a photoresist film 144 is formed on the polyimide layer 142, andexposed and developed to make the embossed pattern corresponding to themaster information signal as shown in FIG. 14(b).

Then, a ferromagnetic film 143 is formed on the polyimide layer 142 andthe protruding portion of the photoresist film 144 by using variety ofmethods such as a vacuum vapor deposition, sputtering, or plating.

Finally, the photoresist film 144 and the ferromagnetic film 143 areremoved by the liftoff method. As a result, the master informationcarrier is obtained as shown in FIG. 14(c), which comprises a substrateincluding the glass base 141 and the polyimide layer (polymer materiallayer) 142, and the protruding portion 143 of the ferromagnetic filmformed on the polyimide layer 142 of the substrate.

The polymer material layer can include a plurality of polymer materialsand is not limited to a single material, considering elasticity,resistance to chemicals, or other properties. A developer for developingthe photoresist film, a remover for liftoff, an etchant for wet etchingand other solutions are usually strong acid or alkaline. The polymermaterial such as a polyimide or a polyamide has an excellent resistanceto acid or alkali and is suitable for the material forming the verysurface of the substrate.

Next, a structure for preventing the master information carrier fromgathering dusts by static electricity in the preformat writing step isexplained. The electrostatic sticking of dust during the preformatwriting step should be suppressed to ensure a secure and uniform contactof the surface of the master information carrier with the surface of themagnetic record disk. If dust sticks to a spot of the surface of themaster information carrier, a deterioration of the S/N ratio of the readsignal or partial lack of read signal may occur at the spot due tospacing loss.

In the master information carrier of the present invention, the polymermaterial that forms at least the surface of the substrate has aconductivity that can prevent the substrate from taking an electriccharge. Thus, the electrostatic sticking of dust to the masterinformation carrier is suppressed and the preformat writing can beperformed with high reliability.

Particles whose main component is a conductive substance may bedispersed in the polymer material that forms at least the surface of thesubstrate. The main component of such particles is preferably a carbon.Such particles whose main component is a carbon can be dispersed easilyin the polymer material and are inexpensive.

As another example of the structure for preventing the electrostaticsticking of a dust, a thin conductive film (e.g., a thin metal film) maybe formed on the surface of the polymer material layer formed on thesurface of the base, wherein a thickness of the conductive film shouldbe thin enough not to obstruct the elasticity of the polymer materiallayer. For example, in the process, the thin conductive film is formedon the surface of the base made of polymer, and the embossed pattern isformed with the ferromagnetic film on the conductive film. Thisconstruction can prevent electrostatic and sticking of dust since thesurface of the master information carrier is made of only conductivematerial.

(Fourth Embodiment)

As mentioned above, it is necessary to ensure a secure and uniformcontact between surfaces of the master information carrier and themagnetic record medium in the writing process of the master informationfor maximizing the effect of the writing method of the presentinvention. If the secure and uniform contact between the surfaces is notobtained, a spacing loss causes a partial lack of a read signal, ordeterioration of S/N ratio due to a small written signal level Inaddition, the magnetic transition may not be sharp at the edges of atrack due to diffusing of the magnetic field for writing, so thatsufficient off-track characteristics may not be obtained.

The master information carrier of this embodiment can ensure the secureand uniform contact between the surface of the master informationcarrier and the surface of the magnetic record medium by a differentconfiguration from that of the third embodiment mentioned above. Asuitable apparatus for writing the master information into a magneticrecord medium with high reliability using this master informationcarrier is also provided.

A first configuration of the master information carrier of thisembodiment has a substrate surface including areas where an embossedpattern corresponding to information signal is formed and areas wherethe embossed pattern is not formed. A ferromagnetic film is formed atleast on surfaces of protruding portions of the embossed pattern, andthrough holes are provided at least partially in the area where theembossed pattern is not formed.

A second configuration of the master information carrier of thisembodiment comprises an area in a surface of a substrate, where anembossed pattern is formed corresponding to information signal, andanother area where the embossed pattern is not formed, wherein a heightof the surface of at least a part of the area where the embossed patternis not formed is lower than that of the area where the embossed patternis formed.

The apparatus for writing an information signal into a magnetic recordmedium using the above-mentioned master information carrier comprisesmeans for forcing the master information carrier and the magnetic recordmedium to contact with each other, means for positioning the masterinformation carrier and the magnetic record medium, and means forapplying a magnetic field for exciting the ferromagnetic film formed onthe surface of the protruding portion of the master information carrier.

A first concrete configuration of the apparatus mentioned above utilizesthe master information carrier having through holes provided at leastpartially in the area where the embossed pattern is not formed, asmentioned above as the first configuration. The apparatus has means toforce the master information carrier (embossed pattern) and the magneticrecord medium to contact securely with each other by sucking air betweenthe master information carrier and the magnetic record medium throughthe through holes after the master information carrier and the magneticrecording medium are contacted with each other.

A second specific configuration of the apparatus mentioned aboveutilizes the master information carrier whose height of the surface ofat least a part of the area where the embossed pattern is not formed islower than that of the area where the embossed pattern is formed, asmentioned above as the second configuration. The apparatus has means toforce the embossed pattern of the master information carrier and themagnetic record medium to contact securely with each other by suckingout air between the area of the master information carrier where theembossed pattern is not formed, and the magnetic record medium after themaster information carrier and the magnetic recording medium arecontacted with each other.

Using the above-mentioned master information carrier and writingapparatus, a magnetic record medium can contact with the masterinformation carrier securely and uniformly. Thus a preformat writing canbe performed with high reliability.

It is preferable that the apparatus comprises a pair of flanges as meansto force the master information carrier and the magnetic recordingmedium to contact tightly with each other, between which the masterinformation carrier and the magnetic record medium are disposed, andmembers for fastening the periphery of the pair of flanges to eachother. If the above-mentioned means with the air suction mechanismfurther comprises these flanges and fastening members, a more secure anduniform contact can be obtained between the master information carrierand the magnetic record medium. When a duct for air suction is connectedto a center portion of the master information carrier or the magneticrecord medium, the suction force may be applied to the center portionstrongly, so that the master information carrier or the magnetic recordmedium may have a warp. In this case, the above mentioned flanges andfastening members suppress the warp so that the master informationcarrier and the magnetic record medium can contact securely anduniformly. It is more preferable to insert an elastic member between oneflange and the master information carrier, and/or, between the otherflange and the magnetic record medium. Thus, the master informationcarrier and the magnetic record medium can contact more securely anduniformly.

The above-mentioned means for alignment of the master informationcarrier and the magnetic recording medium preferably include a markerprovided at the inner circumference or outer circumference of the masterinformation carrier corresponding to the inner circumference or outercircumference of the magnetic record medium.

The following the configurations of this embodiment of the presentinvention in detail, referring to FIGS. 15-21.

FIG. 16 is a cross section showing an example of an apparatus forwriting information signal provided in the master information carrierinto a magnetic record medium. Numeral 161 a and 161 b denote masterinformation carriers, 162 denotes a hard disk, 163 denotes an upperflange, 164 denotes a lower flange, 165 a and 165 b denote permanentmagnets, 166 a and 166b denote air suction devices, 167 a and 167 bdenote three-way valves, 168 a and 168 b denote suction ducts, and 160denotes an O-ring. The magnetization direction of the permanent magnets165 a, 165 b is from back to front of the paper.

The surface of the master information carrier 161 a, 161 b includes anarea 152 disposed once every predetermined angular distance, where afine embossed pattern is formed corresponding to the information signalas shown e.g. in FIG. 15. A part of the area 152 (region B in FIG. 15)is shown enlarged in FIG. 1. As explained in the first embodiment, themaster information provided as an embossed pattern in area 152 includesa tracking servo signal, a clock signal and address information signalthat are disposed sequentially along the track direction. In FIG. 1, thehatched portions are protruding portions whose surface is made of aferromagnetic material such as Co or Ni—Fe.

As mentioned in the first embodiment, a preferable step height betweenthe surface of the protruding potion and the bottom of the embossedpattern corresponding to the information signal varies depending onsurface properties of the magnetic record medium into which the masterinformation is written and the bit size of the master information. Ingeneral, it is more than 0.05 micron, preferably more than 0.1 micron.It was 0.5 micron in one example.

As shown in FIG. 15, the master information carrier 151 has throughholes 153 except at areas 152 where the embossed pattern is formedcorresponding to the information signal. If the substrate of the masterinformation carrier is made of glass, the through holes 153 can beformed by well-known processes such as an ultrasonic process, a laserprocess or wet etching and other methods. It is preferable that adiameter of the through holes is as small as possible and the number ofthe through holes is as large as possible. In an example, through holeswith a diameter of 1.0 mm were disposed in a density of 1.0 per 3.0mm×3.0 mm area by ultrasonic processing.

When writing the master information signal into a hard disk, i.e. amagnetic record medium, centering of the master information pattern andthe hard disk is required before contacting them. To facilitate thiscentering, the master information carrier 151 has markers 154 at theinner circumference as shown in FIG. 15. The marks are formed in samethe step in which the embossed pattern corresponding to the informationsignal is formed. The markers 154 disposed at the inner circumference ofthe master information carrier 151 are aligned to the innercircumference of the hard disk. Alternatively, markers can be disposedat the outer circumference of the master information carrier 151 to bealigned to the outer circumference of the hard disk. If the magneticrecord medium is not a disk having an inner circumference, but amagnetic card or other sheet medium, markers of the master informationcarrier 151 disposed at the outer circumference of the magneticrecording medium may work for alignment. Thus, a position, shape ornumber of the marker should be optimized in accordance with aconfiguration of the magnetic record medium.

FIG. 17 shows a method for writing the information signal formed on themaster information carrier into a hard disk using the writing apparatusshown in FIG. 16. The writing apparatus shown in FIG. 16 utilizes anatmospheric pressure for ensuring a uniform contact in the whole areabetween the master information carriers 161 a, 161 b and the hard disk162. The hard disk is forced to the master information carrier 161 a,161 b when air between the master information carrier 161 a, 161 b andthe hard disk 162 is sucked out via the through holes that are providedin the master information carrier 161 a, 161 b. Thus, the surface of theprotruding portion of the embossed pattern formed on the masterinformation carrier 161 a, 161 b contacts securely with the surface ofthe hard disk 162. Then, utilizing the permanent magnets 165 a and 165b, the ferromagnetic film, formed on the surface of the protrudingportion of the embossed pattern formed on the master information carrier161 a and 161 b, is magnetized to write the information signalcorresponding to the embossed pattern into the hard disk 162, accordingto the steps explained below.

First, by using a permanent magnet 182, the hard disk 162 is previouslymagnetized along the circumferential direction indicated by arrow 181 asshown in FIG. 18. The permanent magnet 182 can be replaced with anelectromagnet. Then, as shown in FIG. 16, an O-ring 160 is set in thegroove of the lower flange 164, on which the master information carrier161 b and the hard disk 162 are stacked on the hard disk 162. At thistime, the previously mentioned markers (154 in FIG. 15) formed on themaster information carrier 161 b should be aligned to the innercircumference of the hard disk 162. Then, another master informationcarrier 161 a and the upper flange 163 with an O-ring 160 set in thegroove are stacked on the hard disk 162. At this time too, markersformed on the master information carrier 161 a should be aligned to theinner circumference of the hard disk 162.

Operating the upper three-way valve 167 a, air between the upper flange163 and the master information carrier 161 a is sucked out by the airsuction device 166 a. At this time, the lower three-way valve 167 bshould be opened so that atmospheric pressure exists in the spacebetween the lower flange 164 and the master information carrier 161 b.When air between the master information carrier 161 a and the hard disk162 is sucked out via through holes 169 provided to the masterinformation carrier 161 a, the hard disk 162 is pressed to the masterinformation carrier 161 a and they are contacted securely with eachother. Then, as shown in FIG. 17(a), the permanent magnet 165 a is movedaround the suction duct 168 a and in parallel to the surface of theupper flange 163 to apply a direct exciting field 171 a. Thus, theferromagnetic film of the protruding portion formed on the masterinformation carrier 161 a is magnetized to write the information signalcorresponding to the embossed pattern into the hard disk 162. The harddisk 162 is previously magnetized along the direction of thecircumference by using the permanent magnet as mentioned above. Thepolarity of this initial magnetization and the polarity of magneticfield applied by the permanent magnet 165 a for writing informationsignal are usually opposite. However, as mentioned in the firstembodiment, it may be preferable that they are the same polarity in somecases. Therefore, the suitable polarity should be selected to achieve afavorable S/N ratio. In an example, they were opposite.

Next, operating the lower three-way valve 167 b, air between the lowerflange 164 and the master information carrier 161 b is sucked out by theair suction device 166 b. At this time, the upper three-way valve 167 ashould be opened so that atmospheric pressure exists in the spacebetween the upper flange 163 and the master information carrier 161 a.When air between the master information carrier 161 b and the hard disk162 is sucked out via through holes 169 formed in the master informationcarrier 161 b, the hard disk 162 is pressed to the master informationcarrier 161 b and they are contacted securely with each other.

As shown in FIG. 17(b), the permanent magnet 165 b is moved around thesuction duct 168 b and in parallel to the surface of the lower flange164 to apply a direct exciting field 171 b. Thus, the ferromagnetic filmof the protruding portion formed on the master information carrier 161 bis magnetized to write the information signal corresponding to theembossed pattern into the hard disk 162. In an example, the polarity ofthe initial magnetization applied to the hard disk 162 and the polarityof magnetic field applied by the permanent magnet 165 b for writinginformation signal were opposite.

As explained above, preformat data is written into both sides of thehard disk 162 in a short time. An electromagnet can be used instead ofthe permanent magnet to magnetize the ferromagnetic film of theprotruding portion formed on the master information carrier. It isdesirable that the material of the upper and lower flanges 163, 164,between the permanent magnet and the master information carrier is anonmagnetic material such as a brass, so that the ferromagnetic film onthe surface of the master information carrier can be magnetized.

If the magnetic record medium is not a hard disk but a flexible disk inthe configuration shown in FIG. 16, and if the through holes formed inthe master information carrier are large, the flexible disk may besucked partially into the through holes and deformed, resulting infailure of preformat writing into correct positions or in lack of signalto be written. Therefore, as mentioned before, it is preferable toprovide as many small through holes as possible. Thus, this apparatuscan write the preformat signal not only into a hard disk but also into aflexible disk with high reliability. The apparatus shown in FIG. 16comprises a pair of master information carriers 161 a and 161 b disposedat both sides of the magnetic record medium, so the preformat writingcan be performed efficiently in a short time for both sides of themagnetic record medium. Thus, productivity is further improved.

FIG. 20 is a cross section showing another example of the apparatus forwriting information signal provided in the master information carrierinto a magnetic record medium. Numeral 201 denotes a master informationcarrier, 202 denotes a hard disk, 203 denotes an upper flange, 204denotes a lower flange, 205 denotes a permanent magnet, 200 a and 200 bdenote elastic plates, 206 denotes an air suction device, 207 denotes athree-way valve, 208 denotes a suction duct, and 209 denotes bolts forfastening the upper flange 203 and the lower flange 204.

The surface of the master information carrier 201 includes an area 192disposed once every predetermined angular distance where a fine embossedpattern is formed corresponding to the information signal as shown inFIG. 19(a). Similarly to the configuration shown in FIG. 15, an exampleof enlarged pattern of this area 192 is shown in FIG. 1.

In the master information carrier 191 shown in FIG. 19(a), compared withthe areas 192 where the embossed pattern is formed and a peripheral area191 (non-hatched area in FIG. 19(a)), the other area 193 (hatched areain FIG. 19(a)) has lower height of the surface. This area 193 is called“lowered area” hereinafter. FIG. 19(b) shows a surface contour of asection of FIG. 19(a) along the phantom curve line C—C′. On the surfaceof the area 192, the embossed pattern is formed corresponding to theinformation signal as shown in FIG. 1. After forming the embossedpattern by photolithography or other method, the lowered area 193 isformed by using a well-known method such as machining, supersonicprocess or laser process. The height difference between the area 192where the embossed pattern is formed and the lowered area 193 ispreferably more than 10 micron, more preferably more than 100 micron,though it depends on the thickness of the substrate of the masterinformation carrier 191.

When writing the information signal formed on the master informationcarrier into a hard disk, i.e. a magnetic record medium, centering ofthe master information pattern and the hard disk is required beforecontacting them. As shown in FIG. 19(a), the master information carrier191 has markers 194 at the inner circumference. The markers 194 arealigned to the inner circumference of the hard disk. Alternatively,markers can be disposed at the outer circumference of the masterinformation carrier 191 to be aligned to the outer circumference of thehard disk.

FIG. 21 shows a method for writing the master information formed on themaster information carrier into a hard disk by using the writingapparatus shown in FIG. 20. The writing apparatus shown in FIG. 20ensures a uniform contact between the master information carrier 201 andthe hard disk 202 not only by utilizing an atmospheric pressure but alsomechanically. There are spaces between the hard disk 202 and the loweredareas 193 of the master information carrier 201. Air in the spaces issucked out for ensuring the secure contact between the hard disk and thearea of the master information carrier where the embossed pattern isformed corresponding to the information signal. Then, utilizing thepermanent magnet 205, the ferromagnetic film, formed on the surface ofthe protruding portion of the embossed pattern formed on the masterinformation carrier 201 is magnetized to write the information signalcorresponding to the embossed pattern into the hard disk 202 accordingto the steps explained below.

First, as shown in FIG. 18, by using a permanent magnet 182, the harddisk 202 is previously magnetized in the circumferential directionindicated by arrow 181. Then, as shown in FIG. 20, the elastic plate 200b, the hard disk 202 and the master information carrier 201 are stackedin turn on the lower flange 204. The elastic plate 200 b has a throughhole at the center, whose diameter is substantially the same as a centerhole of the hard disk 202. At this time, the previously mentionedmarkers (194 in FIG. 19) should be aligned to the inner circumference ofthe hard disk 202. Then, another elastic plate 200 a and upper flange203 are stacked on the master information carrier 201. The elasticplates 200 a and 200 b can be made of a variety of materials such as asilicone rubber.

Operating the three-way valve 207, air between the lowered area 193 ofthe master information carrier 201 and the hard disk 202 is sucked outby the air suction device 206. As a result, the hard disk 202 and thearea of the master information carrier where the embossed pattern isformed contact securely with each other. The suction duct 208 isdisposed at the center of the apparatus as shown in FIG. 20, so anexhaust conductance is large at the center portion of the masterinformation carrier 201. Therefore, the air suction effect is strong atthe center portion but weak at the peripheral portion of the masterinformation carrier 201. Consequently, it is possible that a securecontact between the hard disk 202 and the master information carrier 201is not obtained at the peripheral portion.

To solve this problem, elastic plates 200 a and 200 b are disposedbetween the upper flange 203 and the master information carrier 201 aswell as between the lower flange 204 and the hard disk 202, and inaddition, the peripheral portions of the upper and lower flanges 203,204 are fastened to each other with bolts 209, as shown in FIG. 20.Adjusting the fastening force of each bolt 209, the hard disk 202 andthe master information carrier 201 are contact with each other securelyand uniformly. Thus, the hard disk 202 and the area of the masterinformation carrier 201 where the embossed pattern is formedcorresponding to the information signal are contact with each otheruniformly over a whole surface.

Finally, as shown in FIG. 21, a direct exciting field 211 is applied bymoving the permanent magnet 205 along circumferential direction and inparallel to the surface of the upper flange 203. By this operation, theferromagnetic film of the protruding portion of the embossed patterncorresponding to the information signal is magnetized and theinformation signal is written into the hard disk 202. The hard disk 202is previously magnetized along the circumferential direction by usingthe permanent magnet. The polarity of this initial magnetization and thepolarity of magnetic field applied by the permanent magnet 205 areusually opposite. However, in some cases, the same polarity between themis preferable depending on the embossed pattern formed on the masterinformation carrier. Therefore, the suitable polarity should be selectedfor good S/N ratio of the read signal according to each condition ofapplication. In one example, they were opposite.

It is desirable that a material of the upper flange 203 is a nonmagneticmaterial such as a brass since the upper flange 203 is placed betweenthe permanent magnet 205 and the master information carrier 201.

As mentioned above, the configuration shown in FIG. 20 can obtain a morereliable preformat writing by sucking out the air between the hard diskand the lowered area of the master information carrier, and by fasteningthe peripheral portion of them with the bolts.

The present invention, though explained with several examples, can beutilized in a variety of embodiments. For example, the applications ofthe present invention are not limited to preformat writing of a magneticdisk, but include preformat writing of a magnetic card, magnetic tape,or other magnetic record medium.

The present invention can be applied to writing information signals intoa magneto-optical record medium or other magnetic record media that usea variety of optical effects for reproducing the signal. When writinginformation signal into a magneto-optical record medium by using themethod of the present invention, the magneto-optical record medium maybe heated to the Curie temperature or near the compensation temperatureto perform writing under the condition where the spontaneousmagnetization is vanished. This method is called a “thermo-magneticwriting method” and is advantageous.

Furthermore, the information signal to be written into the magneticrecord medium is not limited to the preformat data such as a trackingservo signal, address, clock and other signals. It is possible to applythe present invention to writing a variety of data, audio, video orother signals. In these applications, mass production of software can beperformed by utilizing the present invention to provide software at lowcost.

What is claimed is:
 1. A master information carrier for writing aninformation signal into a magnetic record medium, wherein an embossedpattern corresponding to the information signal is formed on asubstrate, at least a protruding portion of the embossed pattern iscomposed of a ferromagnetic material layer having a saturation magneticflux density more than 0.8 T, and the ferromagnetic material layercomposing the protruding portion is not continuous between adjacentprotruding portions, but divided by recessed portions.
 2. The masterinformation carrier according to claim 1, wherein an embossed patterncorresponding to a digital information signal is formed on a surface ofthe substrate, a cross section of the protruding portion along bitlength direction of the digital information signal has a substantiallytrapezoidal shape with an upper side at a surface that is shorter than alower side on the substrate, and a length difference between the upperand lower sides is not more than twice the height of the trapezoid. 3.The master information carrier according to claim 2, wherein curvatureradii at edges of the upper side of the trapezoid are not more than ahalf of the upper side length.
 4. The master information carrieraccording to claim 2, wherein a thickness of the ferromagnetic materiallayer at the protruding portion is not more than a half of the upperside length, so that the master information carrier is suitable forwriting information into an in-plane magnetic record medium.
 5. Themaster information carrier according to claim 2, wherein a thickness ofthe ferromagnetic material layer at the protruding portion is more thantwice of the upper side length, so that the master information carrieris suitable for writing information into a perpendicular magnetic recordmedium.
 6. The master information carrier according to claim 1, whereinan embossed pattern corresponding to a digital information signal isformed on a surface of the substrate, and a cross section of theprotruding portion along bit length direction of the digital informationsignal has a substantially trapezoidal shape with an upper side at asurface that is longer than a lower side on the substrate.
 7. The masterinformation carrier according to claim 6, wherein a thickness of theferromagnetic material layer at the protruding portion is not more thana half of the upper side length, so that the master information carrieris suitable for writing information into an in-plane magnetic recordmedium.
 8. The master information carrier according to claim 6, whereina thickness of the ferromagnetic material layer at the protrudingportion is more than twice of the upper side length, so that the masterinformation carrier is suitable for writing information into aperpendicular magnetic record medium.
 9. A master information carrierfor writing an information signal into a magnetic record medium, whereinan embossed pattern corresponding to the information signal is formed ona substrate, at least a protruding portion of the embossed pattern iscomposed of a ferromagnetic material layer having a coercive force notmore than 40 kA/m in the inplane direction, and the ferromagneticmaterial layer composing the protruding portion is not continuousbetween adjacent protruding portions, but divided by recessed portions.10. The master information carrier according to claim 9, wherein anembossed pattern corresponding to a digital information signal is formedon a surface of the substrate, a cross section of the protruding portionalong bit length direction of the digital information signal has asubstantially trapezoidal shape with an upper side at a surface that isshorter than a lower side on the substrate, and a length differencebetween the upper and lower sides is not more than twice the height ofthe trapezoid.
 11. The master information carrier according to claim 10,wherein curvature radii at edges of the upper side of the trapezoid arenot more than a half of the upper side length.
 12. The masterinformation carrier according to claim 10, wherein a thickness of theferromagnetic material layer at the protruding portion is not more thana half of the upper side length, so that the master information carrieris suitable for writing information into an in-plane magnetic recordmedium.
 13. The master information carrier according to claim 10,wherein a thickness of the ferromagnetic material layer at theprotruding portion is more than twice of the upper side length, so thatthe master information carrier is suitable for writing information intoa perpendicular magnetic record medium.
 14. The master informationcarrier according to claim 9, wherein an embossed pattern correspondingto a digital information signal is formed on a surface of the substrate,and a cross section of the protruding portion along bit length directionof the digital information signal has a substantially trapezoidal shapewith an upper side at a surface that is longer than a lower side on thesubstrate.
 15. The master information carrier according to claim 14,wherein a thickness of the ferromagnetic material layer at theprotruding portion is not more than a half of the upper side length, sothat the master information carrier is suitable for writing informationinto an in-plane magnetic record medium.
 16. The master informationcarrier according to claim 14, wherein a thickness of the ferromagneticmaterial layer at the protruding portion is more than twice the upperside length, so that the master information carrier is suitable forwriting information into a perpendicular magnetic record medium.